Paper Sizes Guide
A4 vs Letter explained — ISO and North American paper standards compared
Overview
Paper sizes vary by region, with two main standards dominating: the ISO 216 standard (A4, A3, etc.) used internationally, and the North American standard (Letter, Legal) used primarily in the US and Canada.
Understanding these differences is crucial for printing, document sharing, and international business communications.
ISO 216 Standard (A Series)
ISO A Series
Used worldwide except US and CanadaThe ISO system is based on a 1:√2 aspect ratio. Each size is exactly half of the next larger size when folded parallel to the shorter side.
| Size | Dimensions (mm) | Dimensions (in) | Common Use |
|---|---|---|---|
| A0 | 841 x 1189 | 33.1 x 46.8 | Technical drawings, posters |
| A1 | 594 x 841 | 23.4 x 33.1 | Flip charts, posters |
| A2 | 420 x 594 | 16.5 x 23.4 | Drawings, diagrams |
| A3 | 297 x 420 | 11.7 x 16.5 | Drawings, large tables |
| A4 | 210 x 297 | 8.3 x 11.7 | Letters, documents (standard) |
| A5 | 148 x 210 | 5.8 x 8.3 | Notepads, booklets |
| A6 | 105 x 148 | 4.1 x 5.8 | Postcards, flyers |
North American Sizes
North American Paper Sizes
Used in USA and CanadaNorth American sizes are based on traditional sizes with no mathematical relationship between them.
| Name | Dimensions (in) | Dimensions (mm) | Common Use |
|---|---|---|---|
| Letter | 8.5 x 11 | 216 x 279 | Standard documents |
| Legal | 8.5 x 14 | 216 x 356 | Legal documents |
| Tabloid | 11 x 17 | 279 x 432 | Newspapers, large format |
| Executive | 7.25 x 10.5 | 184 x 267 | Memos, notepads |
| Half Letter | 5.5 x 8.5 | 140 x 216 | Booklets, flyers |
A4 vs Letter: Key Differences
A4 (ISO)
210 x 297 mm
8.27 x 11.69 inches
- Taller and narrower
- Used in 95% of countries
- Part of logical sizing system
- Better for binding
Letter (US)
8.5 x 11 inches
216 x 279 mm
- Shorter and wider
- Used in US, Canada, Mexico
- No standard scaling system
- More landscape-friendly
Tip: When printing PDFs internationally, always check the paper size setting. An A4 document printed on Letter paper (or vice versa) will have incorrect margins!
Common Envelope Sizes
| Envelope | Dimensions | Fits Paper |
|---|---|---|
| C4 | 229 x 324 mm | A4 unfolded |
| C5 | 162 x 229 mm | A4 folded once / A5 |
| C6 | 114 x 162 mm | A4 folded twice / A6 |
| DL | 110 x 220 mm | A4 folded in thirds |
| #10 (US) | 4.125 x 9.5 in | Letter folded in thirds |